Blazor page elements other than Body

Question

I have a Blazor server-side app, trying to understand the structure. Inside the MainLayout.razor page, I see the tag @Body, and this is where each page\'s content is rendere

Answer 1

Here is a more Dynamic solution:

MainLayout.razor

@inherits LayoutComponentBase


    



    

        
    

    

        @Body
    

    

        
    

AppHeader.razor

@implements IDisposable

@LayoutService.Header
@code {
    [Inject]
    public ILayoutService LayoutService { get; set; }

    protected override void OnInitialized()
    {
        LayoutService.PropertyChanged += LayoutService_PropertyChanged;
        base.OnInitialized();
    }

    private void LayoutService_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
    {
        if (e.PropertyName == nameof(ILayoutService.Header))
        {
            StateHasChanged();
        }
    }

    public void Dispose()
    {
        if (LayoutService != null)
        {
            LayoutService.PropertyChanged -= LayoutService_PropertyChanged;
        }
    }

}

ILayoutService.cs

public interface ILayoutService
{    
    RenderFragment Header { get; }    
    SetHeader HeaderSetter { get; set; }
    event PropertyChangedEventHandler PropertyChanged;    
    void UpdateHeader();
}

LayoutService.cs

public class LayoutService : ILayoutService, INotifyPropertyChanged
{

    public RenderFragment Header => HeaderSetter?.ChildContent;

    public SetHeader HeaderSetter
    {
        get => headerSetter;
        set
        {
            if (headerSetter == value) return;
            headerSetter = value;
            UpdateHeader();
        }
    }

    public void UpdateHeader() => NotifyPropertyChanged(nameof(Header));

    public event PropertyChangedEventHandler PropertyChanged;

    private void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
        => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));

    private SetHeader headerSetter;
}

The Setter

SetHeader.cs

public class SetHeader : ComponentBase, IDisposable
{
    [Inject]
    private ILayoutService Layout { get; set; }

    [Parameter]
    public RenderFragment ChildContent { get; set; }

    protected override void OnInitialized()
    {
        if (Layout != null)
        {
            Layout.HeaderSetter = this;
        }
        base.OnInitialized();
    }

    protected override bool ShouldRender()
    {
        var shouldRender = base.ShouldRender();
        if (shouldRender)
        {
            Layout.UpdateHeader();
        }
        return shouldRender;
    }

    public void Dispose()
    {
        if (Layout != null)
        {
            Layout.HeaderSetter = null;
        }
    }

}

Provide the service:

In my case Program.cs

 builder.Services.AddScoped();

Example

@page "/counter"

Counter

Current count: @currentCount

Click me


    
Hello Current count: @currentCount



    
Goodbye Current count: @currentCount


@code {
    private int currentCount = 0;
    private void IncrementCount() => currentCount++;
}

This also clears the values on navigation as I am using IDisposable . The Setter does not have to be set (Null is ok). If more than one setter is used the latest takes precedence. I have not tested dynamically removing multiple setters on one page.

Here is a repo using WebAssembly 3.2.1